Magnet structure



May 9, 1944.

l.. H MATTHIAS MAGNET STRUCTURE Filed Nov. 5, 1941 3 Sheets-Sheet 1 FIG.2.

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INVENTOR @QM #WwW/a ATTORNEY May 9, 1944 1 H, MAT TH|As A ,2,348,556MAGN-ET STRUCTURE Filed Nov. 5. 1941 3 sheets-sheet 3 FIG. I2.

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D 2.7 o 26 BY MM2/a 7W 22 ATTORNEY Patented May 9, 1944 MAGNET STRUCTURELynn Il. Matthias, Milwaukee, Wis., assignor to Allen-Bradley Company,Milwaukee, Wis., a corporation of Wisconsin Application November 5,1941, serial No. 417,907

(ci. zoo-94) 3 Claims.

This invention relates to electromagnetic actuators of the type commonlyemployed for actuating switches, for opening and closing valves, forshifting mechanical control instrumentalities and the like, and residesin an improvement therein in which the relatively attractablc portionsof an electromagnetic eld structure are arranged in relation to amagnetic by-pass which is effective to divert decient closing iiux, buta part only of adequate closing flux when said eld portions are inseparated position and which is ineffective to divert any of the fluxwhen the lleld portions are in attracted position.

Electromagnets employed for actuating switches and the like areordinarily arranged to act'against a bias, caused either by gravity orby resilient reaction, and are usually called upon to hold electricalcontacts in engagement under a substantial amount of contact force. Suchmagnets, furthermore, are called upon to have suicient travel so thatthe contacts can be separated sufficiently to effectively interrupt thecurrent. Such magnets therefore must have a substantial attractive forcesuilicient to overcome the bias over a substantial exciting coil. Ifvthe coil be designed so as to pro,

duce insulcient flux to move the armature at moderately. reducedexcitation voltages-then the attractive force at rated voltage is verylittle more than sufficient for the duty required and the action of themagnet and switch is sluggish.

A further, more important defect of such constructions'is that in acertain range of reduced excitation voltage the armature will moveagainst the bias until the contacts come into engagement and theninsufficient attractive` force is available to cause the armature tomove against the additional bias of the contact backing springs to asealing position. Under these conditions the required contactr forceis'not established and the contacts sometimes overheat to the point ofdestruction.I Little can be done by Strengthening or weakening theexcitation coil to overcome this diiilculty, since strengtheningr thecoil merely further reduces the voltage at which the undesirablecondition occurs,'while further weakening of the coil merely brings theexcitation voltage at which the undesirable condition exists closer tothe rated voltage i the coil,

In the electromagnet of this invention the above dimculty is avoided anda magnet is-provided which will respond only to excitation voltageswhich are high enough to ensure an adequate attractive force suiicientto cause the armature to move to sealing position, thus ensuring thatthe contacts or the like will engage with the full force intended. Themanner in which this desirable result is obtained will be apparent fromthe description which follows. V

This invention is hereinafter described by reierence to the accompanyingdrawings wherein there is set forth by way of illustration and not oflimitation a Specific instance of an embodiment of the apparatus of thisinvention.

In the drawings:

Fig. l is a front elevation of an electromagnet constructed inaccordance with this invention. parts thereof being'shown broken away;

Fig. 2 is a plan view of the magnet shown in Fig. 1:

Fig. 3 is a plan view, in section, viewed through the plane 3-3indicated in Fig. 1;

Fig. 4 is a side elevation, in section, viewed through the plane 4-4 ofFig. 1;

Fig. 5 is a perspective view of the stationary portions of the fieldstructurev of the magnet shown in Fig. 1;

Fig. 6 is a perspective view oi the armature or movable field portion ofthe magnet shown in Fis.y 1;

Fig. 7 is a perspective detail view of the armature guiding sleeve andmagnetic by-pass;

Fig. 8 is a diagrammatic front elevation, in section, showing the magnetparts. in open position under conditions of inadequate excitation. Theux paths are roughly indicated by dotted lines;

Fig. 9 is a diagrammatic front elevation, in section, showing the magnetparts in open position under conditions of adequate excitation. The fluxpaths are roughly indicated by dotted lines:

Fig. 10 is a diagrammatic front elevation, in section,` showing themagnet parts in partially closed position with adequate excitation. The

flux paths occurring under such conditions are roughly indicated bydotted lines;

contact engages the stationary contacts, s

The electromagnet of this invention may be embodied in any oi.' theseveral forms in which a movable part is arranged to be drawn to astationary part in response to magnetic flux established by a coil. Theinvention is herein illustrated and described as applied to theparticular type of such general class of magnet structures which isshown and described in Reissue Patent 20,094, issued September 1, 1936,lupon the application of Gustav O. Wilms and Albert J. Dawe.

I'he magnet type selected to illustrate the invention is shown herein inthe drawings as being provided with a roughly rectangular stationaryiield piece I, composed oflaminations secured together by rivets 2. Thelower side of iield piece I is broken to provide a passage I withinwhich the tongue 4 of a T-shaped armature member l is slidinglyreceived. The T-shaped head of the armature is provided with polemeeting faces l which are positioned to come into engagement with polepieces 'l which project downwardly from the lower side oi the fieldpiece I. The pole pieces I are slotted, as appears more clearly in Fig.5, to accommodate shading rings 8 located as shown in Fig. l2. v

The two outer laminations of the iield piece I 'are formed of materialof substantial thickness and strength and are bent outwardly at 9 and I0to provide means for securing an-armature guide and magnetic by-passassembly made up oi the parts shown more clearly in Fig. '7. The arma-Yture guide and by-pass assembly is in the form of a split rectangularsleeve comprising two identical separable inwardly facing U-shapedparts. Each o! the U-shaped parts is provided with a smooth interiorguiding sleeve portion Il formed o! nonmagnetic material. ProjectingUpwardLv from the upper end of each of the guiding sleeves II is a lugI2 adapted to be accommodated within the outwardly bent portions 9 ofthe outer iield piece laminations. integrally ormed with the lower endsof the sleeves Ii are laterally bent perforated ears Il which areadapted to pass over and surround the downwardly projecting lugs Il,which are formed as a part oi' the outer held piece laminations.

Secured to .the exterior of the sleeves I I are bypass collar segmentsil. The collar segments I are composed of mild steel or other suitablemagnetic material. Above the by-pass collar segments and likewisesecured to the sleeves il are nonmagnetic dummy collars I0 oi' the formand shape more clearly appearing in Fig. 7.

In assembling the magnet, a coil Il is put in place within the centralopening in the field piece of rearrangement of iiux paths which occurswhen the apparatus of this invention is in use. In Fig. 8 the armatureis shown in extreme open position. A magnetic flux path isdiagrammatically indicated as passing through the iield piece I and theby-pass collar segments i5, both of which are stationary parts iixedwith reference to one another. This is the ltype of condition whichprevails in a magnet o! this invention when excitation is less than thatwhich will produce a condition approaching saturation in the by-pass I5.'Ihis quantity of excitation also is a quantity which is lnsumcient toproduce an adequate attractive force i1' it were permitted to act uponthe armature. For example. if line voltage is low andthe coil 20 is thusinadequately excited, the ux circuit is largely confined to thatillustrated in Fig. 8. The by-pass collar segments are constructed ofmaterial having appropriate magnetic properties to permit the carryingof a good part of a maximum inadequate iiux without saturation. Thisreduced quantity of ilux prefers the circuit indicated because thereluctance thereoi' is less than for any ilux circuit passing throughthe armature. In Fig. 9, however, there is diagrammatically indicatedthe flux path conditions prevailing in a magnet of' this invention whenexcitation is increased beyond that for which Fig. 8 is typical. In thiscase, part of the iiux enters the armature and therefrom to the iieldpiece, thus applying an attractive force to the armature. as roughlyindicated by the dotted lines 2|. When excitation is icreased to thepoint where the attractive force exerted upon the armature 5 issufiicient. the'armature moves in response thereto toward i the i'leldpiece I.

I. The sleeve and by-pass assembly is then inserted, thus holding thecoil 20 in place. The tongue I of the armature 5 is then passed into thesleeve until the center lamination of the armature extends through theapertures provided therefor in the upper side ot the iield piece.Assembly bolt Il is then passed through the entire iield structure,sleeve lugs I2, and through an elongated slot Il formed in the upwardlyprojecting center lamination i9. The magnet assembly is thus completedin a form which permits the armature 5 to move between the positionshown in full lines in Fig. 1 and the position shown in dotted linestherein.

The parts of the construction described, which perform magneticfunctions, are the field piece I, the armature 5, and the by-pass collarsegments I5. The relative locations of these parts are diagrammaticallyrepresented in Figs. 8 to 11, in-

With the armature `5 in movement, as soon as the upper end of the tonguel rises above or into the vicinity of the upper level ci the collarsegments IS, a circuit of greatly reduced reluctance passing through thearmature comes into existence. The reluctance of this circuit is farless than for any circuit through the stationary bypass and the iiuxpaths shift to a coniiguration roughly indicated in Fig. 10. Thereuponthe entire attractive force of the magnet becomes effective and thearmature continues to move with substantially increased force until theclosed position shown in Fig. 11 is reached. In the final, or closedposition, the ilux paths become largely established through the courseshown in Fig. 1l.

It will be evident Iroman inspection of Figs. 8 to l1, inclusive, thatexcitation which is suiiicient to place the armature l in motion must besubstantial in amount and therefore will be productive o! a high iinalclosing force, In this way it is possible to design a magnet which isentirely elusive, for the purpose of illustrating the type 76insensitive to low line voltages and, at' the same time, one whichcloses with high attractive force under every condition of excitationwhich is sui'- ilcient to cause a closing movement. Not only areconditions of inadequate closing force thus avoided, but the minimumvoltage at which response is obtained is consistent and remains so overthe life oi' the magnet.

For the actuation o! any instrumentality where substantial travel isrequired, this property o! responding only to adequate excitation is aproperty of decided advantage In the case oi switches, this advantage isof marked importance for reasons which have been stated above. To moreclearly illustrate the cooperation between the magnet of this inventionand spring-backed switch contacts, a magnet oi' this invention is shownin Fig. 12 in relationship to an electric switch. As appears in thisfigure, the upwardly projecting center lamination I9 of the magnetarmature is secured to a thruster bar 22 composed of insulatingmaterial. Mounted upon the thruster bar 22 are upwardly projectingspringbacked contacts, one set of which is shown in the broken awayportion of the figure. 'Ihe movable contacts 23, as appears more clearlyin Fig. 13, are in pairs arranged to bridge between a corresponding pairof stationary contacts 24. The movable contacts 23 are joined by across-bar which is secured to and guided by a telescopic sliding sleeve21. Side guiding supports 25 serve to retain and prevent lateraldisplacement of the movable contacts. A preloaded spring 26 urges thecross-bar of the contacts 23 upwardly against the inwardly turned endsof the guiding members 25. When the armature moves to closed position,the contacts 23 engage the stationary contacts 24 a short distancebefore the travel of the armature is complete. The final movement of thearmature to sealing position thereupon compresses the spring 26, causingthe contact assembly to assume the position shown in Fig. 13, thussetting up the required contact force,

Referring now to Fig. 10, it will be observed that with the magnet ofthis invention it ls possible to provide a spring-backed contact whichis brought into compression only after the armature has moved to thepoint where the by-pass has been eliminated as an instrumentality whichinterferes with the attractive force. Such is the arrangement shown inFig. 12. It is apparent, therefore, that the by-pass I5 need not impairor lessen to any extent the forcefulness of the engagement of thecontacts. While such an ar rangement is of particular value where themagnet of this invention is employed for actuating switches of the typeillustrated, it is, nevertheless possible to apply the magnet of thisinvention to duties Where actual work is done over a much larger portionof the magnet stroke, if such is desired.

While this invention has been herein described by reference to aspecific embodiment of the same, it is intended that the protection ofLetters Patent to be afforded hereby be not unnecessarily limited bysuch description, the intention beingA that such protection extend tothe full limit of the inventive advance disclosed herein as'dened by theclaims hereto appended.

What I claim as my invention is:

1. In a magnetically operated electric switch the combination comprisinga field piece and support, a coil, an armature movable to and from openand closed positions with respect to said field piece and biased to openposition, a pair of contacts one being associated with said armature formovement thereby, the other being associated with saideld support, saidpair of contacts being adapted for yielding pressure engagementthroughout a portion of the travel of the armaure adjacent the closedposition thereof, and a magnetic by-pass disposed along side of aportion of the path of travel of the inner end of said armature adjacentthe open position thereof for diminishing the attractive force exertedupon said armature when in open position, said by-pass terminating shortof that part of travel of said armature within which said contacts areport, a coil, an armature lmovable to and from 'A open and closedpositions with respect to said field piece and biased to open position,a pair of i contacts one being associated with said armature formovement thereby the other being associated with said eld support', aspring disposed to act upon one of said contacts so as to causeresilient yielding engagement between said contacts throughout a portionof the travel of said armature adjacent the closed position thereof, anda `magnetic by-pass disposed along side of a portion of the path oftravel of the inner end of said armature adjacent the open positionthereof for diminishing the attractive force exerted upon said armaturewhen in open position, said bypass terminating short of that part of thepath of travel of said armature within which said contacts are inengagement so as to render said bypass ineiective to diminish theattractive force exerted upon said armature while said contacts are inengagement.

3. In a magnetically operated electric switch the combination comprisinga field piece and support, a coiljan armature movable to and from openand closed positions with respect to said field piece and biased to openposition, stationary contacts associated with said eld support, movablecontacts adapted to engage said stationary contacts, loose connectionmeans im' mounting said movable contacts upon said armature, springsinterposed between said movable contacts and said loose connection meansfor resiliently urging said movable contacts toward the limit ofaccommodation of said loose connection means,

said springs being adapted to be deflected to maintain resilient contactpressure between said stationary andmovable contacts throughout aportion of the armature travel adjacent the closed position thereof, anda magnetic by-pass disposed along side of a portion of the path oftravel of the inner end of the armature adjacent the open positionthereof for diminishing the attractive force exerted upon said armaturewhen in open position, said by-pass terminating short of that part ofthe path of travel of said armature within which said contacts are inengagement so as to render said by-pass ineffective to diminish theattractive force exerted upon said armature while said contacts are inengagement.

